Wikipedia
Nautilus-X
Nautilus-X (Non-Atmospheric Universal Transport Intended for Lengthy United States Exploration) is a multi-mission space exploration vehicle concept developed by engineers Mark Holderman and Edward Henderson of the Technology Applications Assessment Team of NASA.
The concept was first proposed in January, 2011 for long-duration (1 to 24 months) exo-atmospheric space journeys for a six-person crew. In order to limit the effects of microgravity on human health, the spacecraft would be equipped with a centrifuge.
The design was intended to be relatively inexpensive by manned spaceflight standards, as it was projected to only cost US$3.7 billion. In addition, it was suggested that it might only need 64 months of work.